1. Rats were exposed by inhalation to 7 different concentration profiles of carbon tetrachloride. Each profile had a total concentration times time equal to 4500 ppm-hr. Some of the profiles could be distinguished from others based on histopathological changes in the livers. The toxic response was not consistently related to number of, duration of, or interval between pulses. 2. and 3. Studies are underway to determine the mechanism of the acceleration of atherosclerosis by carbon disulfide.